In the letter, tournament referee Andrew Jarrett is believed to have said: "Undergarments that either are or can be visible during play (including due to perspiration) must also be completely white and contain no more than 1cm of coloured trim."

Wimbledon's harsher rules come after some players, including Serena Williams, began to wear bright underwear in recent years.

Serena Williams at Wimbledon 2013

Serena's sister Venus Williams, has spoken out in favour of the stricter dress-code.

"I think it's a nice change. I think everyone just kind of glows in white. Obviously not all year, because anything every day is boring. But during these two weeks, it's nice," she said in an interview after her win on Wednesday.